(i) Field of the Invention
The present invention relates to a fiber optic connector having an optical fiber fixed therein for connecting an optical fiber to an optical device, such as an optical waveguide, and its manufacturing method.
(ii) Description of Related Art
A fiber optic connector wherein optical fibers are fixed to a substrate is used as a fiber optic connector attached to an optical device, such as an optical waveguide.
FIG. 20 is an explanatory diagram of the fiber optic connector disclosed in Japanese Patent Laid Open Publication No. 10-160974.
In this fiber optic connector, only a part of the bare portion 5a and 5b of optical fibers are fixed to a grooved substrate but the other portion of the optical fibers including the coated portion 5b and 6b of upper and lower fiber ribbons 5 and 6 are not fixed to a grooved substrate 1.
As a result, the bare portion of optical fibers easily can be damaged when they touch an edge of the substrate or the like.
Therefore, the coated portion of optical fibers as well as the bare portion of optical fibers in which the coatings have been removed are usually fixed to a substrate in a fiber optic connector.
FIG. 16 shows one example of such a fiber optic connector.
As shown in FIG. 16(A), a part (called xe2x80x9cpart Axe2x80x9d) for fixing the bare portion of optical fibers and a part (called xe2x80x9cpart Bxe2x80x9d) for fixing the coated portion of optical fibers are built onto the substrate 1, fiber arranging grooves 1c are formed in the upper surface of part A 1a, and part B 1b is formed at a different level than part A 1a. 
As shown in FIG. 16(B), in order to fix optical fibers 3 onto a substrate, with the bare portions 3a of the optical fibers 3 arranged in the fiber arranging grooves 1c and pressed down from above by a fiber pressing member 2, an adhesive 4 is injected around the bare portion of the optical fibers between the fiber arranging grooves 1c and the fiber pressing member 2 and also around the bare portion 3a and the coated portion 3b of the optical fibers 3 placed on part B 1b. 
An illustration of the adhesive is omitted from FIG. 16(B).
Usually, the outside diameter of a bare portion 3a of the optical fiber is approximately 125 xcexcm and the outside diameter of the coated portion 3b of the optical fiber is approximately 250 xcexcm.
Therefore, if a step down is built between part A 1a and part B 1b of the substrate so that the difference in the level of the centers of bare portion 3a in the fiber arranging grooves 1c and the level of the upper surface of part B 1b of the substrate is approximately 125 xcexcm, the center of the optical fibers fixed to the substrate will follow an approximately straight line, as shown in FIG. 16(C).
In order to connect to a waveguide or the like, the end faces of the bare portion of optical fibers are ground, usually, at a slant, for example at an angle of 8xc2x0 relative to a plane perpendicular to the axis of the optical fibers so as to reduce the occurrence of reflected light.
However, it is difficult to align the position of the fibers as shown in FIG. 16. If the position of the optical fibers at the rear end of the fiber arranging grooves 1c shifts upward or downward, the bare portion of optical fibers 3a will contact either the rear edge of the fiber arranging grooves 1c or the rear edge of the fiber pressing member 2 resulting in damage to the bare portion of the optical fiber. The bare portion of optical fibers may also be stressed locally by the expansion or contraction of the adhesive due to heat.
The above problems are particularly striking in double-density fiber optic connectors. Here, double-density fiber optic connectors shall mean high-density fiber optic connectors wherein the sequencing density of the optical fibers is set to double the conventional density, for example the connectors described in 1997 Electronic Communication Information Association General Meeting, Preliminary Lectures, Takagi et.al., C-3-15, xe2x80x9cPLC High-Density Double 2xc3x9716 Splitter Module Production.xe2x80x9d
Two optical fiber ribbons, an upper and lower, are used in these double-density fiber optic connectors. The bare portion of optical fibers in the upper fiber ribbon are inevitably raised to form a gap between the bare portion and the substrate.
This gap is then filled with adhesive to set the upper and lower optical fibers, demanding a relatively large amount of adhesive. Therefore, the influence of any expansion or contraction of the adhesive due to heat is greater than in the case of normal density fiber optic connectors.
FIG. 17 shows one example of a double-density fiber optic connector. A fiber arranging groove of half the pitch of the fiber arranging groove 1c shown in FIG. 16 is formed on the substrate 1.
The fiber ribbons 5 and 6 are composed of plural optical fibers having its bare portion (i.e. glass portion) with an outside diameter of 125 xcexcm coated with a protective coating such that their outer diameter becomes 250 xcexcm. The optical fibers are arranged at intervals of 250 xcexcm and covered with a common coating to form a fiber ribbon.
As a result, if the common coating and the protective coating are removed at the tips, the bare portion of optical fibers are aligned with 125 xcexcm gaps between them. By shifting the upper and lower fiber ribbons 5 and 6 apart horizontally by 125 xcexcm and layering them on top of each other, the upper and lower bare portion of optical fibers 5a and 6a fit alternately in their respective gaps. Seen in a planar view, the bare potion of optical fibers 5a and 6a of the upper and lower fiber ribbons are lined up perfectly straight in alternating pairs. But viewed from the side, the bare portion of optical fibers 5a and 6a are bent with their front ends pressed down by the fiber pressing member 2 and fixed to the substrate 1 by an adhesive. In this way, a double-density fiber optic connector is obtained.
FIG. 18 shows a double-density fiber optic connector wherein two upper and two lower fiber ribbons have been attached. In the figure, the fiber optic connector comprises 16 fibers arranged in four fiber ribbons, two above and two below.
However, a fiber optic connector with 32 optical fibers can also be made using eight fiber ribbons each having 4 optical fibers.
If the fiber optic connector of FIG. 18 is observed at in a planar view, the bare potion of optical fibers 5a and 6a of the upper and lower fiber ribbons are lined up perfectly straight in alternating pairs. However, if it is viewed from the side the bare potion of optical fibers 5a and 6a are bent with their front ends pressed down by the fiber pressing member 2 and fixed to the substrate 1 by an adhesive.
FIG. 19 shows the fixed condition of the bare potion of optical fibers in the double-density fiber optic connectors of FIGS. 17 and 18. The tips of the bare portion of optical fibers 5a and 6a of the upper and lower fiber ribbons 5 and 6 are fixed at the same height, but the positions of the bare portion of optical fibers within the upper and lower fiber ribbons differ. As a result, the bare portion of optical fibers 5a of the lower fiber ribbon 5 stretch and extend toward part A 1a of the substrate 1 while bending upward and the bare portion of optical fibers 6a of the upper fiber ribbon 6 extend toward part A 1a of the substrate 1 while bending downward, as shown in FIG. 19(A). The bare portion of optical fibers 5a of the lower fiber ribbon 5 can also be made perfectly straight, but in that case it is necessary to increase the bend in the bare portion of optical fibers 6a of the upper fiber ribbon 6 more than that shown in FIG. 19(A).
In either case, upward and/or downward bends in the fibers result.
If the radius of curvature of these bends is small and the bare portion of optical fibers are fixed in this condition, they may break due to static fatigue.
In order to increase the radius of curvature, it is necessary to lengthen the bare portion of optical fibers 5a and 6a from part A 1a of the substrate 1 to the coated portion 5b and 6b to a certain extent.
However, when the fibers are lengthened the substrate 1 must also be lengthened, which increases costs.
In FIG. 19(B) the bare portion of optical fibers 5a and 6a are portrayed as perfectly straight at the edge of the rear end of the fiber arranging grooves 1c and the edge of the rear end of the fiber pressing member 2. However, since the bare portion 5a and 6a of optical fibers are bent upward and downward respectively as mentioned above, they may be damaged or receive localized stress, if they contact the rear end edges.
As a result, if they contact the rear end edges, the bare portion of optical fibers may be damaged or receive localized stress.
Further, in the fiber optic connector described in Japanese Laid Open Patent Publication No. 10-96836, a construction that prevents breakage of the optical fibers is employed by rounding the edge of the rear end of the fiber pressing member that presses down multiple fibers placed on the fiber arranging grooves to cushion contact with the fibers.
However, the effect on the bare portions of the optical fibers from the rear end edge of the fiber arranging grooves is not improved. In particular, as shown in FIG. 19 of the above Patent, when two layered fiber ribbons are used and fixed such that the bare portion of optical fibers of the lower layer descend, the problem of localized stress on the bare portion of optical fibers is great because they are pushed down by the rear end edge of the fiber arranging grooves.
In both the multiple fiber connector of Japanese Laid-Open Patent Publication No. 9-197193 and the fiber optic connector of Japanese Laid-Open Patent Publication No. 10-10352, localized stress on the bare potion of optical fibers from the rear end edge of the fiber arranging grooves due to the hardening contraction of the adhesive or the expansion and contraction of the adhesive due to a temperature cycle cannot be avoided because the bare portion of optical fibers from which the coating has been removed are in contact with the rear end edge of the fiber arranging grooves. This stress is increased if the arrangement of the fibers is skewed on the fiber arranging grooves during assembly.
FIG. 21 is an explanatory diagram of the stress on the bare portion of optical fibers from the rear end of the fiber arranging grooves. 1 is a substrate, 1a is part A for fixing bare portion of optical fibers, 1b is part B for fixing a coated portion, 3b is a coated portion, and 3a is a bare portion of optical fiber. As shown in FIG. 21(A), if the bare portion of optical fibers 3a of the fiber ribbon are bent downward at the rear end 1a of part A of the substrate 1, the bare portion of optical fibers 3a are locally stressed at the points P shown in FIG. 21(B).
In this way, in conventional fiber optic connectors, the bare portion of optical fibers from which the coating has been removed are fixed using a method such that they are locally stressed by the rear end edge of the fiber pressing member and by the rear end edge of the fiber arranging groove, damage to the fibers increases, and there is a danger this will lead to breakage.
In view of the above-mentioned problems, the present invention is made in order to provide a fiber optic connector that comprises a substrate comprising part A with multiple fiber arranging grooves for fixing bare portion of optical fibers and part B for fixing the remaining portion of the bare portion of the optical fibers and coated portion of the optical fibers, and that can prevent an increase in transmission loss and breakage of optical fibers by reducing the localized stress on the bare portion of the optical fibers from the rear end of a fiber pressing member thereof and the rear end edge of the fiber arranging grooves on the substrate thereof, and its manufacturing method.
A first embodiment of the present invention is a fiber optic connector comprising a substrate and a pressing member, wherein one or more optical fibers are fixed in a manner that at least part of bare portion of one or more optical fibers are fixed with an adhesive under the fiber pressing member and respectively in one or more fiber arranging grooves which are formed on a part of the substrate, and the remaining bare portion of the optical fibers are fixed with the adhesive such that they are stuck in the fiber arranging grooves, which extend to the rear of the fiber pressing member, within a designated range at the rear of the fiber pressing member but gradually separate from the fiber arranging grooves beyond the end of the designated range, and the coated portion of the optical fibers are fixed with the adhesive at a slant position on or above the horizontal surface of the remaining part of the substrate.
A second embodiment of the present invention is a fiber optic connector comprising a substrate having one or more fiber arranging holes, wherein one or more optical fibers are fixed in a manner that at least part of bare portion of the optical fibers are fixed with an adhesive respectively in the fiber arranging holes formed in a part of the substrate and the remaining bare portion of the optical fibers are fixed with the adhesive such that they are stuck in fiber arranging grooves, which are formed continuously to the fiber arranging holes on the part of the substrate, within a designated range at the rear of the fiber arranging holes but gradually separate from the fiber arranging grooves beyond the end of the designated range, and the coated portion of the optical fibers are fixed with the adhesive at a slant position on or above the horizontal surface of the remaining part of the substrate.
The fiber optic connectors according to the first and second embodiments of the present invention differ each other only in their means of fixing the bare portion of the optical fibers: by a fiber pressing member or by fiber arranging holes, but are substantially the same in all other points.
Optical fibers used in the present invention may be either in the form of an optical fiber ribbon or a plurality of single optical fibers separately arranged without a common coating.
The present invention is useful for suppressing the occurrence of localized stress on the bare portion of optical fibers (i.e. the portion of optical fibers in which the coating has been removed) from the fiber pressing member or the fiber arranging holes of fiber optic connectors. Furthermore, even if the adhesive expands and contracts or the position of optical fibers shifts in the fiber arranging grooves, the present invention enables to prevent an increase in loss or damage to the bare portion of optical fibers because there is no such direct contact between the edge of the rear end of part A of the substrate and the bare portion of optical fibers with each other as causes localized stress on the bare portion of optical fibers.
An aspect of manufacturing method of a fiber optic connector according to the present invention is characterized in that one or more optical fibers from which the coatings in their front tips have been removed to expose their glass portion are lowered with an angle of not less than 2xc2x0 maintained between the central axis of the optical fibers and the upper surface of the substrate, and are fixed to the substrate at an angle formed as small as possible, not exceeding 20xc2x0, between the central axis of coated portion of the optical fibers and the upper surface of the substrate in a manner that at least part of bare portion of one or more optical fibers are fixed with an adhesive under the fiber pressing member and respectively in one or more fiber arranging grooves which are formed, extending to the rear of the fiber pressing member, on a part of the substrate, and the remaining bare portion of the optical fibers are fixed with the adhesive such that they are stuck in the fiber arranging grooves within a designated range at the rear of the fiber pressing member but gradually separate therefrom beyond the designated range, and the coated portion of the optical fibers are fixed with the adhesive at a slant position on or above the upper surface of the remaining part of the substrate.
Another aspect of manufacturing method of a fiber optic connector according to the present invention is characterized in that one or more optical fibers from which the coatings in their front tips have been removed to expose their glass portion are lowered with an angle of not less than 2xc2x0 maintained between the central axis of the optical fibers and the upper surface of the substrate, and are fixed to the substrate at an angle formed as small as possible, not exceeding 20xc2x0, between the central axis of coated portion of the optical fibers and the upper surface of the substrate in a manner that at least part of bare portion of the optical fibers are respectively fixed with an adhesive in the fiber arranging holes formed in a part of the substrate and the remaining bare portion of the optical fibers are fixed with the adhesive such that they are stuck in fiber arranging grooves, which are formed continuously to the fiber arranging holes on a part of the substrate, within a designated range at the rear of the fiber arranging holes but gradually separate therefrom beyond the designated range, and the coated portion of the optical fibers are fixed with the adhesive at a slant position on or above the upper surface of the remaining part of the substrate. Thus, a fiber optic connector in which the occurrence of localized stress on the bare portion of optical fibers from the fiber pressing member or the fiber arranging holes is suppressed, can be manufactured as described above. Furthermore, even if the adhesive expands and contracts or the position of optical fibers shifts in the fiber arranging grooves, the present invention enables to prevent an increase in loss or damage to the bare portion of optical fibers because there is no such direct contact between the edge of the rear end of part A of the substrate and the bare portion of optical fibers as causes localized stress on the bare portion of optical fibers.
The above and further objects and novel features of the invention will be more fully clarified from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawing is for the purpose of illustration only and is not intended as a definition of the limits of the invention.